A vexing problem with refrigeration systems is that, under some circumstances, the evaporator coil will have frost accumulate thereon and as the frost thickness increases, the overall efficiency of the system decreases dramatically, energy is wasted and the cost of operating the system increases significantly. The problem is especially acute in the case of heat pumps and commercial refrigeration units; accordingly, many schemes have heretofore been proposed for detecting the frost and for taking corrective action for removing the frost from the outdoor coil. Examples of prior art systems include U.S. Pat. Nos. 3,170,304; 3,170,305; 3,400,553; and 4,209,994.
Our invention comprises an improved apparatus for detecting a frost build up on the evaporator coil of a refrigeration system and for initiating defrost of the system when the frost has accumulated to a preselected magnitude.